Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Freon

Ammonia

Brine

Carbon dioxide

2. The value of C.O.P in vapour compression cycle is usually

Always more than unity

Always less than unity

Equal to unity

Any one of the above

3. Rating of a domestic refrigerator is of the order of

10 tons

5 tons

0.1 ton

40 tons

4. Highest temperature encountered in refrigeration cycle should be

Near critical temperature of refrigerant

At critical Temperature

Above critical temperature

Much below critical temperature

5. The freezing point of sulphur dioxide is

-135.8°C

-77.7°C

-56.6°C

-75.2°C

6. The operating pressure for refrigerating units using R-12 as a refrigerant is

8 bar

30 bar

15 bar

2 bar

7. Freon group of refrigerants are

Nontoxic and non-inflammable

Inflammable

Non-inflammable and toxic

Toxic

8. Which of the following statement is correct?

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(B) The increase in air movement increases the evaporation from the human body.

(D) Both (A) and (B)

9. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Normal cooling

Super-cooling

Sub-cooling or under-cooling

None of these

10. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(A) Heat dissipated to the surroundings

(D) Difference of (A) and (B)

(B) Heat stored in the human body

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11. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Less

Unpredictable

Equally

12. Most thermostatic expansion valves are set for a superheat of

20°C

10°C

5°C

15°C

13. The condition of refrigerant after passing through the condenser in a vapour compression system is

Wet vapour

Superheated vapour

Dry saturated vapour

Saturated liquid

14. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Zero

None of these

Positive

Negative

15. Which of the following cycles uses air as the refrigerant?

Bell Coleman

Stirling

Carnot

Ericson

16. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 3

1: 1

1: 9

9: 1

17. For obtaining high COP, the pressure range of compressor should be

High

Optimum

Any value

Low

18. Cooling water is required for following equipment in ammonia absorption plant

Absorber

Evaporator

Condenser

Condenser, absorber and separator (rectifier)

19. Critical temperature is the temperature above which

A gas will never liquefy

Water will evaporate

Water will never evaporate

A gas will immediately liquefy

20. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

1.2

0.2

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21. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

22. The curved lines on a psychrometric chart indicates

Dew point temperature

Wet bulb temperature

Relative humidity

Dry bulb temperature

23. The domestic refrigerator uses following type of compressor

Piston type reciprocating

Centrifugal

Miniature sealed unit

Axial

24. In a lithium bromide absorption refrigeration system

Lithium bromide is used as a refrigerant and water as an absorbent

Water is used as a refrigerant and lithium bromide as an absorbent

None of these

Ammonia is used as a refrigerant and lithium bromide as an absorbent

25. The bank of tubes at the back of domestic refrigerator is

Evaporator tubes

Capillary tubes

Refrigerant cooling tubes

Condenser tubes

26. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

3.33

1.33

2.33

4.33

27. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

T₂/ (T₂ - T₁)

(T₁ - T₂)/T₁

T₁ / (T₂ - T₁)

(T₂ - T₁)/T₁

28. The minimum temperature to which water can be cooled in a cooling tower is

Dew point temperature of air

Dry bulb temperature of air

Wet bulb temperature of air

Ambient air temperature

29. In a refrigeration system, heat absorbed in comparison to heat rejected is

More for small capacity and less for high capacity

Same

Less

30. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.67

0.6

0.376

0.4

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31. In a refrigeration system, the expansion device is connected between the

Compressor and condenser

Evaporator and compressor

Condenser and receiver

Receiver and evaporator

32. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant pressure

Takes place at constant entropy

Takes place at constant temperature

Involves no change in volume

33. The boiling point of ammonia is

-10.5°C

-77.7°C

-33.3°C

-30°C

34. The vapour compression refrigerator employs the following cycle

Reversed Carnot

Rankine

Carnot

Reversed Rankine

35. The capillary tube, as an expansion device, is used in

All of these

Room air conditioners

Domestic refrigerators

Water coolers

36. A bootstrap air cooling system has

Two heat exchangers

One heat exchanger

Three heat exchangers

Four heat exchangers

37. Which of the following is not a desirable property of a refrigerant?

High risibility with oil

Good electrical conductor

Low boiling point

Large latent heat

38. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

1.25

2.15

5.12

39. A thermostatic expansion valve in a refrigeration system

Maintains different temperatures in evaporator in proportion to load

Ensures the evaporator completely filled with refrigerant of the load

Is suitable only for constant load systems

None of the above

40. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Superheat the vapour

Collect vapours

Detect liquid in vapour

Collect liquid refrigerant and prevent it from going to compressor

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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